Enamelware is comprised of a steel material, cast iron, aluminum, copper material, stainless steel, or other metal material forming a substrate on the surface of which a glass-like enamel layer is formed. It is produced for example by forming the metal substrate into a predetermined shape, then applying a glaze (frit) to the surface and firing at a high temperature. This enamelware is resistant to surface flaws, enables oily dirt etc. to be easily removed, and is superior in heat resistance, acid resistance, and alkali resistance, so is being used for kitchen products, diningware, sanitary vessels, interior and exterior materials of buildings, and other broad applications.
Further, in air preheater elements or casing members of power plants, casing members or ducts of civilian use boilers or garbage incinerators, and other applications as well, in addition to the conventionally used sulfuric-acid and hydrochloric-acid dew-point corrosion-resistant steel materials and weather-resistant steel materials and other corrosion resistance steel materials (for example, see Japanese Patent No. 3699669), an enameled steel material comprised of a substrate formed by a steel material on the surface of which an enamel layer is provided is being used. In general, the steel material used as a substrate for an enameled steel material is equivalent to ordinary steel in corrosion resistance. To use enamelware comprised of enameled steel materials for these applications, the bondability between the substrate and enamel layer, fishscale resistance, resistance to bubbles and black spot flaws, and other enameling characteristics and workability have to be excellent.
As art for improving the enameling characteristics, in the past the method has been proposed of making the arithmetic surface roughness (Ra) of the surface of the steel sheet forming the substrate 0.5 to 5 μm and making the mean space (Sm) of surface relief 30 to 300 μm so as to improve the bondability with an enamel layer (for example, see Japanese Patent Publication (A) No. 2005-344141). Further, in the past, an enameling use steel sheet improving both the enameling characteristics and workability by setting suitable steel ingredients (for example, see Japanese Patent Publication (A) No. 2002-80934 and Japanese Patent No. 3643319). For example, the enameling use steel sheet as described in Japanese Patent Publication (A) No. 2002-80934 reduces the C content to a specific amount or less, sets suitable contents of Si, Mn, P, S, Al, N, B, and O, and further sets (N present as BN)/(N present as AlN) to 10.0 or more. Further, Japanese Patent No. 3643319 discloses an enameling use steel sheet having a deep drawability equal to or better than Ti-containing steel by reducing the C content to a specific amount or less, setting suitable contents of Mn, Si, Al, N, O, P, S, and Cu, and further adding suitable quantities of Nb and V.